Measuring instrument.



A. NICOL.

MEASURING INSTRUMENT.

APPLICATION FILED APR. 11, 1913.

1,098,916, Patented June 2,1914,

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Inventor: o ucgust. Nicol,

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UNITED STATES PATENT OFFICE.

AUGUST NICOL, 0F NIEDERr-SCHGNHAUSEN, GERMANY, ASSIGNOR TO GENERALELECTRIC COMPANY, A CORPORATION OF NEW MEASURING INSTRUMENT.

Specification of Letters Patent.

Patented June 2, 1914.

Application filed April 11, 1913. Serial No. 760,453.

To all whom it may concern.

- Be it known that LAoousr Nrcon, a subject of the King of Prussia,residing at Nieder Schonhausen, Germany, have invented certain new anduseful Improvements in Measuring Instruments, of which the following isa specification.

-My invention relates to measuring instruments having adisk or armaturein which eddy currents are generated by the rotation of the disk in amagnetic field.

The invention is particularly adapted for use in. a speed measuringinstrument, in which a rotatable disk is retarded or braked by. a fixedmagnet, and the retarding or braking action, .which is proportional tothe speed to be'measured, is transmitted to an indicating pointerthroughsuitable instrumentalities. 1.. r

. A measuring instrumentdependent for its action upon eddy currentsgenerated in a closed circuit, such as a disk or armature of lowelectricalresistance, is accurate only at thei'temperature'at-which itis calibrated, since the high temperature coeflicient of copper, andsimilar lowv resistance metals, causes marked variations in theelectrical resistance of those metals as' the temperature varies, This.error is particularly objectionable in speed measuring instruments-whichare subjected to widely varying temperatures while in use.

The object of my invention is to provide a simple, inexpensive andreliable means for compensating for changes in temperature in measuringinstruments which are dependent for their action on eddy'currentsgenerated in a disk or armature of conducting material.

In carrying out my invention, I arrange a rotatable disk within thefield of influence of a retarding or braking magnet whose effectivebraking moment with respect to the disk is adapted to be varied by atemperature responsive device, such as a thermostatic member.

The novel and patentable features which I believe to be characteristicof my invention are definitely indicated in the claims appended hereto.

- The construction and mode of operation of a speed measuring instrumentembodying my invention will be understood from the following descriptiontaken in connection with the accompanying drawings, in which:

Figure 1 is a front elevation of a measuring instrument embodying thenovel features of my invention, and Fig. 2 is a sectional view taken onthe line 2-2 of Fig. 1.

Although my invention is useful in connection with any measuringinstrument dependent for its operation on eddy currents generated in ametallic disk, I have illustrated the invention embodied in a speedindicator. It will, however, be understood that this application of myinvention is merely for the purpose of illustration, and

I do not desire to limit the application of my invention. to speedmeasuring instruments.

The speed measuring instrument which I have shown in the drawingscomprises a me tallic disk or armature 5 rotatably mounted between thepoles of two fixed permanent magnets 7 An auxiliary magnet 8 having itsoppositely ositioned poles 9 arranged on opposite sides of the disk 5 isrigidly secured to a pivoted shaft. 10. An arm 11 is rigidly secured tothe. shaft 10 and is operatively connected to a bi-metallic thermostaticmember 12 of semi-circular configuration. By reference to Fig. 2 of thedraw ings, it will be observed that one end of the termostatic member issecured to a fixed part 13 of the instrument, while the other end ispivoted to a link 14. The link 14 is also pivotally connected to the arm11.

It will be readily observed from the drawings that the auxiliary magnet8 is,so arranged that the distance between its poles 9 and the axis ofrotation of the disk 5 can be varied. The effective braking moment 01;the magnet 8 with respect to the disk 5 is adjustable by varying thedistance between the poles of the magnet and the axis of the disk. Theoperative connection between the pivoted magnet 8 and the thermostaticmem ber 19, thus provides an automatic adjustment of the distance betwenthe poles of the magnet and the axis of thedisk, which if properlydesigned is sufiicient to compensate for the errors due to changes intemperature.

Reference to Fig. 1 of the drawings will explain the arrangement of theother operative elements of the speed measuring instrument with therotatable disk 5. The disk 5 is rigidly secured to a pivoted shaft 15 towhich is also secured one member 16 of a. differential gearing. Theothermember 1'; of the differential gearing is loosely mounted on a pivotedshaft 18. The planetary gear member 19 of the differential gearing isloosely mounted on an arm 20, and the arm 20 is rigidly secured to theshaft 18. A control spring 21 is also secured to the shaft 18 andnormally tends to maintain the shaft 18 and planetary gear member 19 inan initial or zero position. An indicating member or pointer 22 issecured to the shaft 18 and is arranged to sweep across a suitable scale23.

The operation of the device is briefly as follows: The gear member 17 isadapted to be driven by a shaft 24 which is rotated at a speedproportional to the speed to be measured. The rotation of the gearmember 17- is transmitted to the disk 5: by the planetary gear'member 19and the gear member 16. The rotationof the disk 5 in the magnetic fieldproduced by the magnets 7 and 8 generates eddy currents within the diskand the disk is 'retarded or braked in the well known manner. Thisretarding action causes the planetary gear member-19 and arm 20 to turnthrough a small angle and until the opposing tension-0f the spring 21equals the braking action ofthe magnets on the disk 5. At this point thepointer 22 comes to zero, and=its position on thescale 23 is anindication of -thel'speedfto-be measured. The" thermostatic member 12 isresponsive to and influenced; by changes in temperature and .operatesto: turn the an);- iliary braking magnet-8 about-its pivot upon changesin temperature? 'The effective braking moment of the magnet with respectto the disk is thus varied and the variation so produced is designed-tocompensate the instrument for'errors'due to changes in temperature, so-that the indications of the instrument are accurate-at alltemperatures.

While I have illustrated two-fixed magnets and an adjustable 'magnet, itwill be understood that other arrangements may be employed withoutdeparting from the spirit of my invention.- I do'not wish, therefore, tobe limited to the details of construction herein illustrated anddescribed by way of example. I, accordingly, aim inthe appended claimsto cover all modifications within the spirit and scope of my invention.

What I claim as new and desire to secure by Letters Patent of the UnitedStates, is

1. A measuring instrument comprising a metallic disk rotatably mounted,a braking magnet positioned to retard the rotation of said disk, andtemperature responsive means arranged to adjust the relative location ofthe magnet and disk'to vary the effective braking moment of said magnetwith respect to said disk to compensate for changes in temperature. p

2. A measuring instrument comprising a metallic disk rotatably mounted,a magnet positioned to retard the rotation of said disk, means formounting said magnet so that the distance between the poles of themagnet and the axis of the disk can be varied, and a thermostatic memberoperatively related to said magnet. P

3. A measuring instrumentcomprising a metallic disk rotatably mounted,*a' pivoted braking magnet having its poles positioned on opposite sidesof said disk, and a thermostatic member operatively related to saidmagnet and adapted to turn the: magnet about its pivot to compensate theeffective braking action of the magnet on the'disl for changes intemperature.

4. A measuring instrument comprising a metallic disk rotatably mounted,a magnet having oppositely positioned poles arranged on opposite sidesof the disk, means for mounting said magnet so that the distance betweenthe poles of the magnet and the axis of the disk can be varied, and athermostatic member operatively'connected to said magnet and adaptedto'vary-the distance'between the poles of the magnet and the axis of thedisk to compensate for changes in temperature. 1

" 5. A measuring instrument comprising means for producing a magneticfield, a metallic disk rotatably. mounted .in said field,

a pivotally 'mounted magnet arranged :to J

retard the rotation of said disk, and athermostatic memberoperativelyarranged to turn said magnet about its pivot for changing the effectiveretarding moment of said magnet on said disk upon changes intemperature. 0

6. A measuring instrument comprising a metallic disk rotatably mounted,a magnet positioned to retard. therotation of said disk, means formounting said magnet so that the effective retarding-moment of the polesof the magnet with respect to the disk is adjustable, and a temperatureresponsive device operatively related to said magnet and adapted toproduce such adjustment of the poles of the magnet with respect to thedisk to compensate for changes in temperature.

7 A measuring instrument comprising means for producing a magneticfield, a metallic disk rotatably mounted in said field, a magnetpositioned to retard the rotation of said disk, means for mounting saidmagnet so that the distance between the. poles of the magnet and theaxis of the disk can be varied, and a th rmostatic member opera tivelyrelated to said magnet and adapted to vary the distance between thepoles of the magnet and the axis of the disk to compensate for changesin temperature.

8. A measuring instrument comprising means for producing a magneticfield, a metallic disk rotatably mounted in said field, a magnet havingoppositely positioned poles arranged on opposite sides of the disk,means for mounting said magnet so that the distance between the poles ofthe magnet and the aXis 'of the disk can be varied, and a thermostaticmember operatively related to said magnet and adapted to vary thedistance between the poles of the magnet and the axis of the disk tocompensate for changes in temperature.

9. A measuring instrument comprising means for producing a magneticfield, a metallic disk rotatably mounted in said field, a

magnet having oppositely positioned poles arranged on opposite sides ofthe disk, a pivot about which said magnet is arranged to turn so thatthe distance between the poles of the magnet and the axis of the diskcan be varied, a thermostatic member having one end secured to a fixedpart of the instrument, and means operatively connecting the other endof the thermostatic member to the magnet so that the magnet is caused toturn about its pivot by said thermostatic member upon changes intemperature.

In witness whereof, I have hereunto set my hand 1913.

AUGUST NICOL.

Witnesses KARL SGHMIEDEL, ALFRED HERMANN,

Copies of this patent may be obtained for five cents each, by addressingthe "Commissioner of Patents, Washington, D. C."

